Searching for Human Brain Specializations with Structural and Functional Neuroimaging
James K. Rilling, Emory University
Humans are truly an exceptional species with respect to cognition. Compared with other primate species, we excel at language, theory of mind, reciprocal exchange, manufacture and use of tools, cultural learning, mathematics, and artistic expression. What are the distinctive attributes of the human brain that support these abilities and how did this miraculous organ evolve? We have attempted to answer these questions by comparing the brains of humans, apes and monkeys with structural and functional brain imaging. Specifically, we have used Diffusion Tensor Imaging to compare white matter fiber tracts involved in human language across these three groups, and we have used Positron Emission Tomography (PET) to compare resting brain glucose metabolism in these same three groups, as a window onto resting state cognition. DTI results show that the pathway linking Wernicke’s and Broca’s brain language areas in humans also exists in apes and monkeys, however the human pathway is more extensive and more lateralized than that of apes or monkeys. Patterns of resting brain activity are quite similar in humans and apes, with both species engaging medial prefrontal regions that, in humans, are consistently linked with reflecting on mental states of others. However, humans differ from apes in having left lateralized activity within language-related cortex at rest, implying that the human resting state is fundamentally different from that of apes insofar as humans think with words. Comparative studies such as these will help us elucidate the neural substrates that support human cognitive specializations.
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